Thirteen longtailed macaques originally were immunized with a recombinant vaccinia virus expressing SIVMne gp160 and boosted with subunit pg160. These animals, together with naive controls, were challenged with various cell-free preparations of the homologous virus by the intravenous or intrarectal route. Last year studies with intravenously challenged animals were completed and the animals were euthanized. Results from this study, combined with those of another project ("Immunogenicity of Recombinant Vaccinia Virus Expressing Envelope Glycoproteins"), demonstrated the differential pathogenicity of E11S virus vs. uncloned SIVmne and also demonstrated the protective efficacy of immunization. The remaining 12 animals, which were challenged with uncloned SIVmne by the intrarectal route, are being held for rechallenge studies.